Camshaft adjusters are generally used in valve train assemblies of internal combustion engines to vary the valve opening and closing times, whereby the consumption values of the internal combustion engine and the operating behavior in general may be improved.
One specific embodiment of the camshaft adjuster, which has been proven and tested in practice, includes a vane adjuster having a stator and a rotor, which delimit an annular space, which is divided into multiple working chambers by projections and vanes. A pressure medium may be optionally applied to the working chambers, which is supplied to the working chambers on one side of the vanes of the rotor from a pressure medium reservoir in a pressure medium circuit via a pressure medium pump, and which is fed back into the pressure medium reservoir from the working chambers on the particular other side of the vanes. The control of the pressure medium flow, and thus the adjusting movement of the camshaft adjusting device, takes place, e.g., with the aid of a central valve having an complex structure of flow-through openings and control edges, and a valve body, which is movable within the central valve and which closes or unblocks the flow-through openings as a function of its position.
One problem with camshaft adjusters of this type is that the camshaft adjuster is not yet completely filled with pressure medium in a start phase or may even have been emptied, so that, due to the alternating torques applied by the camshaft, the rotor may execute uncontrolled movements relative to the stator, which may result in increased wear and an undesirable noise development. To avoid this problem, it is known to provide a locking device between the rotor and the stator, which locks the rotor in a rotation angle position with respect to the stator which is favorable for startup when the internal combustion engine is turned off. In exceptional cases, for example if the internal combustion engine stalls, it is possible, however, that the locking device does not properly lock the rotor, and the camshaft adjuster must be operated with an unlocked rotor in the subsequent start phase. However, since some internal combustion engines have a very poor start behavior if the rotor is not locked in the central position, the rotor must then be automatically rotated into the central locking position and locked in the start phase.
Such an automatic rotation and locking of the rotor with respect to the stator are known, for example, from DE 10 2008 011 915 A1 and from DE 10 2005 011 916 A1. Both locking devices described therein include a plurality of spring-loaded locking pins, which successively lock into locking gates provided on the sealing cover of the stator when the rotor rotates and which each permit a rotation of the rotor in the direction of the central locking position before reaching the central locking position while blocking a rotation of the rotor in the opposite direction. After the internal combustion engine has warmed up and/or the camshaft adjuster has been completely filled with pressure medium, the locking pins are forced out of the locking gates, actuated by the pressure medium, so that the rotor is subsequently able to properly rotate with respect to the stator to adjust the rotation angle position of the camshaft.
One disadvantage of the approach described therein is that the automatic locking is always active only during a rotation of the rotor in one direction, i.e., the rotor is automatically locked only during a rotation from an “advance” or “retard” stop position in the direction of the central locking position. An automatic locking of the rotor from both “advance” and “retard” stop positions in the direction of the central locking position is not possible using the locking devices described therein.